Process for the manufacture of globular smokeless powder



PRUCESES FOR THE f /EANUFACTURE 0F i GLGBULAR SMOKELESS POWDER John Joseph GNeiil, in, Roxana, IlL, and Gilbert E. Cox,

Madison, Gonm, assignor's to @lin Mathieson Chemical.

(Iorpora tion, a corporation of Virginia No Drawing. Application June 21, 1954 Serial No. 438,304

2 Ciaims. or. 52-20 This invention relates generally to the manufacture of propellent powder, and, particularly to the manufacture of spherical and near spherical grains of smokelesspowder.

In United States PatentNo. 2,027,114, granted January 7, 1936, there is disclosed a process of manufacturing smokeless powder wherein droplets of lacquer, composed of smokeless powder base and solvent, are solidified while suspended ina non-solvent medium. Such a process of manufacturing propellent powder has come to be known among those skilled in the art as the globular powder process. der process so as to produce grains having various physical and chemical properties is further disclosed in United States Patents Nos. 2,160,626, "granted May 30, 1939,

2,213,255, granted September 3, 1940, and 2,375,175, granted May 1, 1945. These patents disclose variations in the basic technique of manufacturing globular powder whereby to control the character, uniformity, and ballistic properties of the powder produced. While the globular on a mass scale.

While it has heretofore been recognized that, in the globular powder process, the average grain size in a given batch is controlled to some extent by the violence of agitation during the sizing phase of the process-the more vio lent the agitation, the smaller the grains and vice versa-- such control has very definite limits, and prior to our invention, it was not possible to produce batches wherein a substantial percentage of the product was both well- The technique of controlling the globular powshapen (i. e., very'nearly spherical) and of a diameter greater than twenty-five thousandths of an inch. To accomplish the production of substantial'yields (in a given batch) of globular powder grains having a diameter of thirty-thousandths of an inch or more, our application aforesaid contemplated the use of lacquer of a viscosity so high that the particles would not round up by the techniques disclosed in the aforesaid patents as previously practiced in the art.

In the course of our experience with such high viscosity lacquers, in the manufacture of large grains, we discovered that outer increments of many of the resulting grains were physically diiferent from the internal increments thereof. The grains seemed to have undergone a sort of case-hardening before they were completely rounded or before they were completely solidified; and it is .the object of our invention to overcome this.

Our study of such case-hardened grains finally led us to suspect the cause to be that the suspending medium til) hunch, we discovered that if the suspending liquor be.

pro-charged with a small amount of the same solvent employed in making the lacquer, the case-hardening tendency is diminished; and if the point be ascertained where the solvent content of the suspending liquor is such that the forces tending to draw solvent from thelacquer toward the suspending liquor are in equilibrium with the forces tending to draw solvent from the suspending liquor toward the globule of lacquer, then the finallyhardened globular grains are of homogeneous material.

Accordingly, the invention contemplates fortifying the suspending liquor, employed in the globular powder process, with solvent before pre-formed lacquer is contacted with the suspension liquor. The solvent with which the suspending liquor is fortified is preferably the same as the solvent used for dissolving the smokeless powder base in making the lacquer. For example, when a lacquer composed of three parts ethyl acetate and one part nitrocellulose is suspended in Water, some ethyl acetate will migrate throughthe interface into the water until suificient ethyl acetate is dissolved in the water that equilibrium is establishedthus the lacquerbodies are robbed of solvent unless the water is fortified with ethyl acetate before being contacted by the lacquer. Where the lacquer is of a relatively high solvent ratio, the loss to the suspending liquor of enough solvent to establish equilibrium may be unimportant, but where, for reasons of economy or otherwise (as in the case of making grains of +0.030 diameter), the lacquer is of relatively high viscosity (low solvent ratio), the loss to the suspending liquor of enough solvent to establish'equilibrium may so stiffen the exterior increments of the lacquer particles that they will not round.

Consequently, the invention contemplates predetermination of the amount of solvent necessary to be added to a given suspending liquor in order to establish equilibrium with .a given lacquer which is intended to be suspended in the given suspending liquor. In view of the many variables involved in the globular powder process, we have not devised a formula whereby the equilibrium point may be calculated under any and all conditions which might be encountered in practice; it being quite sufiicient, for

our purposes, to ascertain the equilibrium point by testing samples of the given lacquer and liquor. Accordingly, for any given set of conditions, take a small sample of the suspending liquor which is to be used and a small sample of the lacquer which is to be used; add to the sample of suspending liquor, say, two percent of ethyl acetate (or whatever solvent is in the lacquer); mix the lacquer with the solvent-fortified-liquor sample in the same proportions as the liquor to lacquer ratio in the contemplated operation; after about a minutes' mixing, separate enough liquor for analysis and ascertain the ethyl acetate content thereof; if it is two percent, the first guess was right; if it is three percent, repeat the test fortifying a sample of suspending liquor with three percent the suspending liquor is about the minimum fortification necessary to approach equilibrium. In the sample test ing, it is preferable to approach the equilibrium point from below and as described, thus to ascertain the minimum fortification at which the suspension liquor shows I Patented Apr. 15, 1958 aseqsse 3 no gain in solvent upon mixing with the lacquer. In this connection it is pointed out that the solvent content of the suspending liquor, in order to establish such equilibrium, may be, and usually is, considerably less than the amount of solvent which the suspending liquor is theoretically capable of dissolving. Fortification in excess of the equilibrium value is disadvantageous, particularly when it is desired to manufacture grains of large size, in that the suspension loses stability and the lacquer globules tend to disintegrate. Instead in our efforts to produce large size grains, we have observed such disintegration almost immediately'after contact of presized lacquer bodies with water containing six percent of ethyl acetate.

While the invention is of particular importance in the manufacture of large size grains by the globular powder process, it is also advantageous in the manufacture of smaller grains except by the species of globular powder process wherein the lacquer is actually made in the presence of the suspending liquor in that species the suspending liquor is inevitably saturated with solvent in the process of making the lacquer out of suspended solvent and solid powder base. Since the major utility of the invention resides in its use in connection with the 111211111 facture of large globular grains, the following specific example illustrates the proportions and procedure followed in the making of a batch of globular powder grains wherein more than seventy percent was within the size bracket of 0.034 to 0.041 inch in diameter and well rounded.

The lacquer to be employed consists of a suitable powder base, such as nitrocellulose, dissolved in a solvent which is substantially immiscible with the chosen suspending liquor; if the suspending liquor is to be water, ethyl acetate is an appropriate solvent for the powder base. As an illustrative example, the lacquer may be made up of 135 parts (by weight) of ethyl acetate to 56 parts of dry nitrocellulose (or 80 parts of water wet nitrocellulose). Additives, whether soluble or insoluble are preferably introduced to the ethyl acetate before the latter is mixed with the nitrocellulose. For example, the 135 parts of ethyl acetate may contain /8 part of chalk and /2 part of diphenylamine. The solvent is preferably heated to a temperature of 50 C. before the nitrocellulose is added thereto. It is preferable to add tl e nitrocellulose gradually to the solvent and continue the mixing during the addition until a homogeneous lacquer results.

The suspension liquor to be used with the lacquer above-described, is made as follows: 14 parts gum-arabic are added to 50 parts of water and mixed until the gumarabic has dissolved; the gum-arabic solution is then filtered into 700 parts of water, heated to 50 C. and thoroughly mixed. If it is desired to produce grains substantially without internal pores, 27 parts of sodium sulphate may then be dissolved in the mixture, but care should be exercised so that the sodium sulphate does not cake on the mixing vessel.

From previous experience with lacquer and with suspending liquor as above-described, we have ascertained that 15 parts of ethyl acetate need be added to the abovedescribed suspending liquor in order that solvent equilibrium exists when the above-described lacquer is dis persed therein. Accordingly 15 parts of ethyl acetate are added to the above-described suspension liquor.

Prior to contact, one with the other, the lacquer and the suspension liquor are elevated to a temperature of about 60 C.

The lacquer is subdivided into bodies of the desired size, as by extruding'and slicing in the manner disclosed in our oo-pending Serial No. 361,428, filed June 12, 1953, now U. S. Patent No. 2,740,705 granted April 3, 1955, or

otherwise, so that the lacquer bodies remain suspended I in the suspending liquor throughout the balance of the process. Such presizing and suspension may be accom plished in the mannerdisclosed in the co-pending application of Ralph L. Cook and Eugene A. Andrew, Serial No. 460,014, filed October 4, 1954.

After the lacquer is subdivided and the presized bodies suspended, the mixture is kept under agitation sufiicient to maintain the state of suspension until the suspended presized bodies of lacquer become rounded under the action of the forces of interfacial tension; and during the period of such shaping, the viscosity of the lacquer in the suspended bodies may be reduced as by increasing the temperature or by the addition of solvent as described in our co-pending application, Serial No. 148,742, to render the suspended bodies more responsive to the interfacial tension forces tending to round them. After the suspended bodies have assumed the desired near-spherical shape, the suspension is maintained while they are hardened by driving off the solvent in the manner disclosed in the aforesaid applications and patents. During the hardening step, the solvent is vaporized either by ncreasing the temperature within the still or by reducing the pressure thereof to the point where the solvent, such as ethyl acetate, will vaporize from the system while the lacquer bodies are maintained in suspension.

While the embodiment just described is such as to yield a high percentage of large size grains, it will be understood that by presizing the lacquer particles to a smaller size, the described procedure is applicable to the manufacture of globular powder grains of less than 0.025 diameter. Where high viscosity lacquer is employed, and the presizing accomplished by extruding'and slicing, the size of the final grains may be controlled within closer limits than in cases where the subdivision is accomplished by agitation, but the use of high viscosity lacquer makes it necessary to guard against the robbery of solvent from the lacquer by the suspending liquor which latter is accomplished by the present invention.

From the foregoing description, those skilled in the art should understand the mode of operation of the'invention and realize that it accomplishes its objects. As the globular powder process is subject to many variations in practice, the specific embodiment above-described is to be taken as merely illustrative of the manner in which the invention is utilized, and not as suggesting that the stated proportions of the several components, or the techniques of handling them, are not subject to change as conditions dictate, without departing from the spirit of the invention or the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. in the manufacture of globular powder by the process wherein a smokeless powder base is dissolved in a solvent to form a lacquer, and the lacquer is sub-divided and suspended in a suspending medium which is substantially immiscible with the lacquer, the improvement which comprises fortifying the suspending medium'with said solvent in an amount such as to substantially establish equilibirum with the solvent in said lacquer when the said two are contacted, and thereafter introducing the sub-divided lacquer bodies into said fortified suspending medium. v

2. In the manufacture of globular powder grains, the process Comprising plasticizing smokeless powder base material with ethyl acetate to form fluid lacquer, thereafter suspending the fluid lacquer into a suspending liquor consisting substantially of water, said suspending liquor at the time the lacquer is introduced thereinto being'prefortified with ethyl acetate in the proportions of about 15 parts of ethyl acetate to about 750 parts of water, and solidifying the lacquer in the said suspending liquor.

References Cited in the file of this patent UNITED STATES PATENTS 

2. IN THE MANUFACTURE OF GLOBULAR POWDER GRAINS, THE PROCESS COMPRISING PLASTICIZING SMOKELESS POWDER BASE MATERIAL WITH ETHYL ACETATE TO FORM FLUID LACQUER, THEREAFTER SUSPENDING THE FLUID LACQUER INTO A SUSPENDING LIQUOR CONSISTING SUBSTANTIALLY OF WATER, SAID SUSPENDING LIQUOR AT THE TIME THE LACQUER IS INTRODUCED THEREINTO BEING PREFORTIFIED WITH ETHYL ACETATE IN THE PROPORTIONS OF ABOUT 15 PARTS OF ETHYL ACETATE TO ABOUT 750 PARTS OF WATER, AND SOLIDIFYING THE LACQUER IN THE SAID SUSPENDING LIQUOR. 